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At issue is the question of consent from subjects in photographs, as well as when users add email addresses, names and other details about friends and strangers.

European privacy expert Joe McNamee said that add-your-friends e-mail blasts, frequent in social networking sites, may violate European privacy laws.

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"The receiver didn't want the messages, and the sender didn't realize they were going out," McNamee told the Associated Press. "You would have to search long and hard for someone who would see consent in there."

Particularly controversial have been unilateral attempts by the two companies to expose user data with little consent. Facebook has drawn criticism for its news feed, Beacon advertising platform and recent privacy policy changes. Google has received criticism for Buzz, its new social networking service, and some features in Google Maps.

Facebook does allow you to remove yourself from photos you've been tagged in, but only after the fact. European regulators would probably prefer to see features like that "opt-in" rather than "opt-out" -- as in, the photo wouldn't appear until all subjects consent.

Companies like Google are working on facial recognition software that could make the process of finding people in photos automated, and it already blurs faces captured in Street View, with varying results.